The present invention relates to a direct contact type multiple pressure stage steam condenser system which is suitable for a geothermal turbine plant.
A technique in which a multiple pressure stage steam condenser system is formed by supplying, in a series mode, cooling water to a plurality of steam condensers and in which the cooling power of the cooling water is effectively utilized thereby to improve the thermal efficiency of a turbine plant is well known in the art and is currently employed for heat power plants.
However, for the aforementioned geothermal turbine plant, it is often difficult to obtain a sufficient amount of cooling water because of local conditions at the plant. Therefore, a technique in which a cooling tower is provided to recirculate the cooling water has been extensively employed in such geothermal turbine plants. In this case, in view of economical considerations including the cost of installing and operating the cooling tower, the temperature rise of the cooling water in the steam condensers is, in general, selected to be higher than that for a technique in which the used cooling water is simply discharged as for surface type steam condensers in a conventional heat power plant. Accordingly, for a geothermal turbine plant using cooling water under such concitions, employment of a multiple pressure stage steam condenser system is effective and advantageous for improving thermal efficiency. In addition, a geothermal turbine typically employs direct contact type steam condensers because recovery of the condensate is unnecessary in order to eliminate corrosion and contamination of heat transferring surfaces due to impurities contained in geothermal steam.
FIG. 1 shows an example of a conventional multiple pressure stage steam condenser system which combines a plurality of direct contact type steam condensers as described above. The multiple pressure stage steam condenser system includes a geothermal steam supplying pipe 1, a turbine inlet valve 2, a double-flow turbine 3, a generator 4, a high vacuum stage steam condenser 5, a low vacuum stage steam condenser 6, a cooling water supplying pipe 7, a cooling water discharging pipe 8, a series connection pipe connected between the hot well of the steam condenser 5 and the cooling water supplying inlet of the steam condenser 6, pumps 10 and 11, gas extracting pipes 12 connected to the steam condensers 5 and 6 for extracting non-condensable gas therefrom, and vacuum pumps 13 for extracting gas.
The steam supplying pipe 1 is coupled to a steam well 14. The cooling water pipes 7 and 8 are connected to a cooling tower 15. The two direct contact type steam condensers 5 and 6, which are independent of one another, are juxtaposed as shown in FIG. 1. The steam condensers 5 and 6 are coupled to the discharge side of the double-flow turbine 3 and are coupled to each other through the series pipe 9 and the pump 10 thus forming a multiple pressure stage steam condenser system having two stages, namely, high and low vacuum stages.
The operation of the multiple pressure stage steam condenser system thus constructed will be briefly described. Water cooled by the cooling tower 15 is supplied through the cooling water supplying pipe 7 to the high vacuum stage steam condenser 5 to condense steam discharged through one of the steam discharging outlets of the turbine 3. The mixture of the cooling water and the condensate pooled in the hot well of the steam condenser 5, which is pressurized by the pump 10, is supplied to the low vacuum stage steam condenser 6 to condense steam discharged through the other steam discharging outlet of the turbine 3. The water pooled in the hot well of the steam condenser 6 is returned through the pump 11 to the cooling tower 15 where it is cooled to be supplied again. In this manner, the water is circulated. Non-condensable gas separated in the steam condensers 5 and 6 is extracted and discharged by the vacuum pumps 13 so as to maintain high pressure in the steam condensers.
In the above-described conventional direct contact type multiple pressure stage steam condenser system, in order to supply as cooling water the mixture of the condensate pooled in the hot well of the high vacuum stage steam condenser 5 and the cooling water to the low vacuum stage steam condenser 6, it is necessary to compensate the difference between the pressures of the two steam condensers 5 and 6. That is, it is necessary to further pressurize the mixture by the pump 10. Thus, because power is required for operating the pump 10, the total power consumption is increased. In addition, the total cost of equipment such as pumps, control devices and security devices is increased. This in turn reduces the economical effect of employing a multi-stage steam condenser system.